Very different staining reagents of the type of the present invention are already known which enable blood cells to be identified and characterized by a stain which enables the cells to be labelled or stained after incubation under chosen time and temperature conditions.
Such reagents generally make use of a fluorescent stain or a non-fluorescent stain which, after incubation, enables the stained cells to be counted. This counting may be carried out with manual staining under a microscope, with external staining or with staining using an automated apparatus.
Automated counting is generally carried out by a so-called flow cytometry technique which proves to be more reliable and more rapid than manual counting.
Various stains are already known which are used for the determination of blood cells, in particular reticulocytes, and which may be used for manual or automated counting.
these fluorescent or non-fluorescent stains include pyronine Y, acridine orange, thioflavine T, thiazole orange, new methylene blue, brilliant cresyl blue etc.
Examples of staining reagents are described in particular in the following patent publications: CA 2 024 166, U.S. Pat. No. 5 501 954, U.S. Pat. No. 4 325 706, U.S. Pat. No. 5 438 003, U.S. Pat. No. 5 075 556, U.S. Pat. No. 4 996 040, U.S. Pat. No. 4 883 867, EP 0 545 314, EP 0 545 315, EP 0 430 719, EP 0 215 461, EP 0 226 272 and EP 0 114 462.
In the particular case of the determination of reticulocytes, which are precursors of erythrocytes or mature red corpuscles, the stain serves to color or label the residual RNA contained in the cell.
One of the disadvantages of known staining reagents is that they require a long incubation time, which makes them difficult to use not only in manual techniques but especially in automated techniques.
In particular, thiazole orange requires an incubation time of the order of 30 minutes at room temperature when it is reacted with 5 microlitres of blood.
This incubation time is much too long to enable the process to be completely automated.